TAPPER: He's the mastermind of the deadly terror attack at a museum in Tunisia that killed dozens of tourists and now the Pentagon says they believe they killed him in an airstrike. The frightening reason why the military said they could not wait to act any longer.

Stay with us. We're back after this.

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TAPPER: Welcome back to THE LEAD. I'm Jake Tapper.

New details just coming in in our world lead. The Pentagon confirming U.S. aircraft destroyed an ISIS training camp in Libya.

[16:35:01] The Pentagon claims this action may have stopped plans for a future terrorist attack. Manned and unmanned aircraft were involved in this strike, the Pentagon says.

The target: two houses, according to a U.S. official, in the northwestern city of Sabratha, not far from the Tunisian border.

Libyan television aired images from the aftermath. Nothing but rubble appears to remain.

The U.S. believes its main target, a top ISIS operative, is likely among the dead. That target, Noureddine Chouchane. U.S. officials believe Chouchane was behind two deadly massacres against westerners in Tunisia last year.

Let's go to CNN's Barbara Starr in touch with her sources at the Pentagon.

Barbara, what's the latest about this attack?

BARBARA STARR, CNN PENTAGON CORRESPONDENT: Well, Jake, in fact this was indeed one of the deadliest attacks the U.S. has conducted against ISIS ever, but a U.S. official tells me this was not a typical terrorist training camp.

(BEGIN VIDEOTAPE)

STARR (voice-over): A suspected ISIS camp in Libya now destroyed by U.S. warplanes on the orders of President Obama. U.S. intelligence believes foreign fighters there were training to launch an attack possibly in Europe or Africa. It's only the second time the U.S. has gone after ISIS inside Libya. This time just days after the president warned the U.S. would strike.

BARACK OBAMA, PRESIDENT OF THE UNITED STATES: We will continue to take actions where we've got a clear operation and a clear target in mind.

STARR: With 5,000 ISIS operatives in Libya, the threat of an attack from there is growing.

JOSH EARNEST, WHITE HOUSE PRESS SECRETARY: The president will make good on his promise to continue to apply pressure to ISIL leaders who threaten the United States and our interests.

STARR: Two U.S. F-15s from the U.K. and drones from Italy flew to Sabratha on the North African coast of Libya. This video claims to show the aftermath of the U.S. dropping bombs on four buildings that the U.S. said housed 60 ISIS operatives. U.S. military and intelligence agencies had watched the camp for weeks. Aerial reconnaissance flights saw advanced weapons and tactics training.

A top ISIS operative Noureddine Chouchane at the camp was targeted and killed. He is said to be responsible for two deadly attacks over the border in Tunisia last year.

EARNEST: This individual is a known ISIL leader, a facilitator, and an individual who has facilitated the flow of foreign terrorist fighters across North Africa.

STARR: The U.S. concern now, Libya with no central government in control is a fully functioning third front for ISIS, along with Iraq and Syria, a place they may use to plot attacks against the West.

(END VIDEOTAPE)

STARR: And the U.S. is making it very clear it may have more targets in mind in Libya. What they are looking for are specific ISIS targets. In this case, they actually had a plan to strike twice, Chouchane and also the training camp. When he suddenly showed up at the training camp, they were able to get both targets in one mission -- Jake.

A U.S. official saying the strike was ordered just in case because of a possible terrorist attack that was being planned. What do you know about any potential plot and where these terrorists may have been looking to strike?

PHIL MUDD, CNN COUNTERTERRORISM ANALYST: Look, the U.S. military, the president, the CIA are not going to wait for a plot, Jake. What they're looking at is the fact that they have already seen capability. This is a leader and a group that went across the border into Tunisia, remember that attack on the beach resort that left so many British citizens dead.

You couple that with the refugee problem. This is Libya. A lot of people going across the Mediterranean into Europe, that is into Italy. The fact that the group wants to strike European targets and the fact that they have access geographically to Europe means that the Americans aren't going to wait for a specific plot. They're going to say, as soon as they see this leader in a location, we're taking him out preemptively.

TAPPER: Is this going to be the new normal, preemptive strikes?

MUDD: I think it has to be the new normal with one asterisk. That is if you go back to the pre-9/11 plotting, people after that, my generation of CIA officers are going to say, we're not going to wait for a group that expresses an intent to attack the West to attack. We're going to take them out as soon as we get information, especially if you're dealing in all these areas like Yemen and Libya that don't have a local military that can deal with the problem themselves.

What you've got to worry about in this case is making sure you understand the environment well enough to ensure that there's actually plotting afoot. You don't want to go in too early and stir up the bee's nest and you don't want to go in too late and wait for them to stage an attack before you -- before you go in preemptively.

[16:40:06] TAPPER: How much of an effect is this death of the senior operative going to have when it comes to ISIS?

MUDD: I'd say step back before you make dramatic interpretations of this one event. And that is, this group has a few thousand people in Libya. Moammar Gadhafi was ousted in 2011, five years ago. This group over the past year has taken over geography. If we count success as eliminating one leader, you miss one of the key lessons of the counterterrorism business, that is pace of operations. Take them out every 60 days, every 90 days, every 120 days.

My question for the operators would not be whether this operation was a success, it will be over the course of let's say a year or two or five years, do you maintain a pace of operations over the leaders who follow so that they cannot replicate this leadership in the ISIS organization in Libya. TAPPER: And, Phil, you talk about is controlling wide swaths of

territory in Libya, specifically in northwestern Libya. This was just one ISIS training camp. How many others could be in that area?

MUDD: Well, you've got to look at that term training camp. This is pretty significant. You're talking about potentially 40 plus people, pretty large in terms of training for terror facilities.

But if you look at training camps elsewhere in places like Pakistan and places like Yemen, you might just have a walled compound where six people are training with a local commander. Those people, as I mentioned earlier, could enter the refugee flow into a place like Italy.

So, if you just ask the question not where are 40 plus people congregating as we saw in this case but what's the likelihood in this swath of territory that ISIS controls that there's maybe walled houses where five people are training, there could be a lot of those, Jake, because that's just too easy to hide from Western intelligence.

TAPPER: All right. Phil Mudd, thank you so much.

MUDD: Thank you.

TAPPER: As family and friends say good-bye to Justice Scalia, and you're looking at live pictures there, the White House is starting to give the first real insights into where President Obama stands on picking a nominee and when we could learn a name.

Then, she gave us the literary classic "To Kill a Mockingbird." We'll remember the great author Harper Lee who passed away, next.

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TAPPER: Welcome back. You're looking at live pictures from the U.S. Supreme Court where the body of late Justice Antonin Scalia is lying in repose at the great hall of that building at this hour.

About an hour ago, President Obama and First Lady Michelle Obama stopped by to pay their respects to the late justice. Conservatives have jumped on the president for not planning on attending Scalia's funeral tomorrow.

The White House says President Obama going to the Supreme Court today felt like a more personal way to pay his respects. Also a rare and poignant moment today, all eight other justices not wearing their robes standing together saying good-bye to their friend and their colleague.

CNN justice correspondent, Pamela Brown, is outside the court where thousands of people have been streaming in and out to say farewell.

Pamela, obviously a very moving event today, Justice Scalia having obviously touched a lot of lives. Maybe some of our viewers don't know his bestfriend on the court was liberal Justice Ruth Bader Ginsburg. PAMELA BROWN, CNN JUSTICE CORRESPONDENT: That's right, Jake. They were best buddies on the bench. Scalia called them the odd couple because they had such different ideologies, looked at the law so differently, but they rode elephants together, they went parasailing together and they were best of friends.

What was interesting here today was that people showed up to pay their respects like the ones behind me in line and not all of them share Scalia's conservative ideology, but they said they wanted to come here and pay their respects because Scalia was such an influential judge.

He really changed the way people looked at the law and he dedicated 30 years of his life to service.

(BEGIN VIDEOTAPE)

BROWN (voice-over): On this somber afternoon at the high court, President Obama and the first lady arrived to pay their respects to Justice Antonin Scalia. The first couple paused at the flag-draped casket as Scalia's former clerks stood guard. They'll be taking turns through the day and night. One of his clerks, Jamison Jones.

JAMISON JAMES, FORMER SCALIA CLERK: It was a really touching ceremony this morning. Justice Scalia was a brilliant mentor, but also a warm and kind and generous person.

BROWN: This morning, Supreme Court police officers carried the conservative icon on his final journey to the high court. Behind the casket, some of Scalia's favorite law clerks.

Dozens more lined the marble steps waiting at the massive bronze doors of the court, Scalia's children, grandchildren and his son, a Catholic priest.

Father Paul Scalia led the casket into the great hall where the eight remaining justices said goodbye to their colleague and friend.

UNIDENTIFIED MALE: My brothers and sisters, Jesus says come to me all you who labor and are burdened and I will give you rest.

BROWN: When the private ceremony ended, the public filed in. Two people of particular note, Patty Millette and Sri Srinivasan, considered top contenders to be the president's nominee to replace Scalia.

Another striking moment, the actor who portrayed Scalia in the play "The Originalist" teared up as he stood at the casket. Outside members of the public braved the cold for their turn.

JEFF DALEY, ATTORNEY: As attorneys, as officers of the court, I think we have an obligation to come pay our respects.

BROWN: At a memorial outside, a jar of applesauce and broccoli, referencing Scalia's colorful comments he made during the affordable care cases. A tribute to the justice famous for his humor on the bench. [16:50:05]UNIDENTIFIED MALE: It's a sad time for me personally and for the country. It's tough to imagine this court without him, without him sitting up there for the next argument.

(END VIDEOTAPE)

BROWN: And you're looking at live pictures right now of people waiting to go inside to pay their respects. In fact people started ling up here as early as 6:50 this morning to have an opportunity to go inside. Now the doors will stay open an extra hour later until 9:00 tonight.

Meantime, we've learned the president will be working overtime this weekend reading materials about any potential nominees to fill Scalia's vacancy.

When we asked the White House how many people were on the short list, they basically said we don't have a short list, but there are more than two names we're looking at. Back to you.

TAPPER: All right, Pamela Brown, thank you so much. The Money Lead now. With oil prices cratering, 2015 was a difficult year for the industry. It still pays to be the CEO.

Take for example, the head of oil drilling firm, Slumber Jay, this company says CEO Paul Kibsgard (ph) received total compensation worth $18.3 million last year, all while the company hemorrhaged cash and cut 25,000 jobs, about 20 percent of its workforce. But it's not as if the CEO didn't suffer. He made $18.5 million the year before.

Think the walking dead is scary? You should see the zombies in Washington. Congress knows all about them and is doing nothing to stop them. We'll explain, next.

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TAPPER: Welcome back to THE LEAD. I'm Jake Tapper. Here in Washington, D.C., there are zombies living amongst us. The undead continuing to live on long after they were supposed to have vanished from this earth.

But I'm not talking about apocalyptic creatures here. These zombies are government programs. We'll explain in our latest installment of "America's Debt and The Economy."

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TAPPER (voice-over): The last time Congress authorized funding for the National Weather Service was 12 years before Hurricane Katrina.

The last time funding for the Federal Election Commission was authorized, Ronald Reagan was the one who had been elected.

Why does it matter that these programs and hundreds more are well past their expiration dates? Well, those deadlines were built in to force Congress to re-evaluate and improve the programs before reauthorizing them.

KEVIN KOSAR, THE R STREET INSTITUTE: This is one of those laws that Congress sets up that only applies to itself, so when it breaks its own law, who's going to punish them?

TAPPER: With no real political consequences for Congress skipping the re-evaluation process, the government allows these programs to operate kind of like zombies. They're well past their expiration date yet Congress still lets them feast on government cash.

KOSAR: Skipping the authorization process means that government is mindlessly expanding programs that should be reviewed to see whether if they are truly effective.

TAPPER: The so-called zombie programs are the result of Congress' broken spending machine, $310 billion will go to zombie programs this year alone, according to the Congressional Budget Office.

KOSAR: The failure to kind of look at programs and to be willing to unplug those that don't work is just contributing to the debt problem.

TAPPER: The biggest zombie budget item is for expired Veterans Affairs bills. More than $61 billion worth going to health care programs. Now, the last time that budget was properly authorized was 1998. The same year some of our current service members were born.

BERNIE SANDERS (D), PRESIDENTIAL CANDIDATE: Do you believe the VA needs more funding?

TAPPER: Of course, once Congress heard of the VA scandals, as broken by CNN in 2014, there was plenty of attention.

RICK WEIDMAN, VIETNAM VETERANS OF AMERICA: The question is, is there enough resources for veterans health administration and we have to say we don't know.

TAPPER: But those congressional hearings, like so many others, were only held after the damage was done. The $611 billion worth of programs will join the ranks of the undead by October 1st. And in all likelihood, they'll continue running through the streets without being looked at again by Congress.

Though, Senate Budget Committee Chairman Mike Enzy (ph) reacted to the CBO report with a novel idea. Quote, "Congress should re-examine what we're actually funding in order to improve or eliminate government programs not delivering results," he said. You think?

(END VIDEOTAPE)

TAPPER: Finally today we lost a literary legend. Harper Lee, the author of "To Kill A Mocking Bird" has died. She was 89 years old early this morning. The family of the woman originally named Neel Harper Lee confirmed the beloved writer passed away in her sleep. There will be a private funeral service in the coming days. Her Pulitzer prize-winning book "To Kill A Mockingbird" is one of the most celebrated novels of all time, selling more than 40 million copies worldwide and taught in high school for decades. It also inspired the classic film starring Gregory Peck as Atticus Spinch.

UNIDENTIFIED MALE: Our courts are great levelers, and in our courts all men are created equal. I'm no idealist to believe firmly in the integrity of our courts and in our jury system.

(END VIDEOTAPE)

TAPPER: A play version of "To Kill A Mockingbird" is also currently in the works. For many people, her inspiring writing resonates more than ever in this divisive world in which we live, as Lee wrote in the voice of scout, there's just one kind of folks, folks. Rest in peace, Harper Lee.

Don't forget to watch "STATE OF THE UNION" at 9 a.m. Eastern this Sunday for special coverage after the South Carolina Republican primary and the Nevada Democratic caucuses. That's it for "THE LEAD." I'm Jake Tapper, turning you over to Wolf Blitzer in THE SITUATION ROOM.